The present invention relates to an electromagnetic signal-horn particularly adapted to be used on motor vehicles or motor cycles of any kind.
The known electromagnetic signal-horns comprise a generator of sound waves, referred to as propulsor unit, which is coupled to an acoustic amplifier generally consisting of an amplifying duct having the shape of a horn.
More particularly the propulsor unit comprises an electromagnet adapted to vibrate at a predetermined frequency a membrane free to carry out an alternative motion generating a sound wave addressed to the amplifying duct. The amplifying duct is generally wound as a volute to limit the total dimension of the horn and comprises a first length with a substantially constant section provided with an inlet for the sound signal generated by the oscillating membrane and a second length with variable section according to a substantially conical exponential rule ending with an outlet for the amplified sound signal.
In operation at each actuation of the signal-horn, the electromechanical propulsor unit causes the membrane to oscillate generating sound waves which travel through the entire amplifying duct and are emitted amplified.
More particularly the amplifying duct operates as an acoustic amplifier of selective type, with the pass band centered on the frequencies that can be better heard by the human ear.
As above mentioned said signal-horns are used on motor vehicles and are generally installed individually or as a couple inside the engine compartment. Signal-horns of different features are available on the market and are divided into three categories according to their size: small size or mini horn with diameter 80 mm, mid size diameter 90 mm and medium high size diameter 100 mm, the latter being almost exclusively installed on trucks for their cost and dimensions.
The acoustic performance as to the sound level of said horns is proportional to the dimensions both of the propulsor unit and the amplifying duct.
The need to optimize space and reduce dimensions of each component of the motor vehicle, led to reduce as much as possible the dimensions of the signal-horns, but trying to keep both the sound power and distribution of frequency within the values set by the regulations and required for the approval of the motor vehicle type.
A first drawback of the known horns is due to the fact that by reducing the dimensions of the horn, the levels of sound pressure generated by the horn are considerably reduced, and sometimes do not reach the minimum values required by the regulations especially when individually installed.
Indeed the acoustic performance of these horns are proportional, as hereinbefore mentioned, to the dimensions of both the propulsor unit and the amplifying duct.
This drawback is generally solved by installing a couple of horns however doubling both the overall dimensions of the equipment and its cost or installing single horns of bigger dimensions.
Another drawback is due to the fact that the manufacturer is obliged to impose constrains of installation of the horn in order to make up for the limited level of sound pressure.
More particularly it is necessary to install the horn in such a way that sound propagation occurs without reflections and obstacle, thus in the most exposed positions. However this predisposes the horn to possible damages due to water-sprays or projection of stones and mud.
An object of the present invention is to overcome said drawbacks.
More particularly a first object of the invention is to provide an electromechanical acoustic signal-horn that has dimensions equivalent to those of the small size signal-horns but can develop a sound power equivalent to that developed by signal-horns of bigger size.
Another object is to provide a signal-horn having a manufacturing cost lower than the horns of known type but with the same performances.
Another object of the invention is to provide a horn that can be installed without specific installation constrains.
The above mentioned objects are attained by an electromagnetic signal-horn the main features of which are according to claim one.
Advantageously the signal-horn of the invention develops an acoustic power which is almost the double in comparison with the acoustic power developed by the known horns of the same dimensions.
Still advantageously the invention allows to reduce the costs of installing the horn because there are no special constrains of installation of the horn.
The above mentioned objects and advantages will be better understood by the following detailed description of a constructional preferred embodiment of the invention given as an illustrative but non-limiting example and with reference to the accompanying sheets of drawings in which: